This invention concerns sulfur plasticizing compositions which comprise both an aromatic polysulfide and a linear aliphatic polysulfide. In particular, this invention concerns the use of olefinic-type unsaturated carboxylic acids to moderate hydrogen sulfide evolution during the reaction of sulfur with sulfur plasticizing compositions comprising both an aromatic and a linear aliphatic polysulfide.
Elemental sulfur has been proposed for use in a variety of applications such as coatings, foams, adhesives, and the like, but the development of many of these applications has been hindered by the propensity of sulfur to revert rapidly to its crystalline form. Many additives have been suggested to modify elemental sulfur to produce sulfur-based materials with "plastic" properties. Nearly all of these plasticizers are polysulfides.
The aromatic polysulfides and the linear aliphatic polysulfides are two of the most widely used classes of sulfur plasticizers. U.S. Pat. No. 4,026,719, granted May 31, 1977, describes sulfur-based compositions containing a mica filler and a plasticizing material which have been found to be unexpectedly strong. One of the recommended plasticizing materials comprises a mixture of aromatic and aliphatic polysulfides.
Aromatic polysulfide sulfur plasticizers are generally prepared by the base-catalyzed reaction of an aromatic compound and sulfur. In some instances, the reaction product is neutralized with acid, but in many cases the unneutralized product is used in combination with a linear aliphatic polysulfide. It has been found that, when a sulfur-plasticizing composition comprising an unneutralized aromatic polysulfide prepared by base catalysis and a linear aliphatic polysulfide are contacted with molten elemental sulfur, hydrogen sulfide gas is evolved at such an extremely rapid rate that conventional gas scrubbers cannot function satisfactorily and some noxious fumes are liberated to the atmosphere.
The evolution of hydrogen sulfide gas, which occurs when the plasticizer composition is contacted with molten sulfur, significantly limits the manufacture of plasticizer compositions comprising an aromatic polysulfide and a linear aliphatic polysulfide.